WASHINGTON (CNN) -- The Obama administration believes it will reach a deal with the government of Afghanistan that would allow American troops to remain in the country after the current NATO mission ends next year, the top U.S. diplomat in the region said Thursday.

The disclosure follows reports this week the administration was seriously considering an option of leaving no forces in the country after 2014.

"We do not believe that that's the likely outcome of these negotiations," James Dobbins, special envoy for Afghanistan and Pakistan, told the Senate Foreign Relations Committee.

Pressed about reports on the so-called "zero option," Dobbins labeled them "unbalanced and unhelpful."

A Pentagon official testifying at the same hearing said the United States will continue working with the Afghan government on establishing a security agreement as well as training Afghan forces.

"The United States is transitioning in Afghanistan, not leaving," Peter Lavoy, acting assistant secretary of defense for Asian and Pacific security affairs said.

U.S. and Afghan officials have been discussing plans to keep a small force behind to fight insurgents and to train Afghan security personnel.

Dobbins said President Barack Obama is reviewing options for the number of American forces that would stay in Afghanistan 18 months from now.

"We've made significant progress on the text of a new bilateral security agreement. Of course, without an agreement on our presence in Afghanistan, we would not remain," he said.

A sticking point reported this week involves apparent tension over Afghan President Hamid Karzai.

Karzai has said he would like American forces to remain, but also has been highly critical of them over the years after incidents in which U.S. forces have killed civilians.

The U.S-Afghanistan relationship was also tested after news last month the United States and the Taliban planned peace talks. In response, Karzai cut off negotiations on the residual troop presence.

Dobbins said there was not much of a parallel between the situation in Iraq when U.S. military operations ended and the current scenario in Afghanistan.

"Unlike Iraq, to which comparisons are often made, the Afghans actually need us to stay. Most Afghans want us to stay. And we have promised to stay," he said.